Optical device for semiconductor based lamp

ABSTRACT

This invention discloses an optical device for a semiconductor based lamp, the optical device comprising a base for mounting a semiconductor based light-emitting device thereon, a transparent body encapsulating the semiconductor based light-emitting device, and a reflective surface covering a predetermined region on a top of the transparent body, the reflective surface having an opening exposing the transparent body, wherein light emitted from the semiconductor based light-emitting device transmits through the opening of the reflective surface.

BACKGROUND

The present invention relates generally to electrical lighting devices, and, more particularly, to an electrical lighting device utilizing light emitting diodes (LEDs).

A Light-emitting diode (LED) is a semiconductor diode based light source. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. When used as a light source, the LED presents many advantages over incandescent light sources. These advantages include lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability.

However, LED as light source has its disadvantages. One of the disadvantages is that the light emitted from a LED chip concentrates in a direction normal or perpendicular to the surface of the LED chip, i.e., LED light is strong in the upright direction and drastically diminished in the sideway directions. In order to make a LED light more like a traditional incandescent light source with uniform light emitting intensity in all directions, reflectors has been used to redirect the LED beam from upright to sideways. However, redirecting light merely sacrifices light in the upright direction in favor of sideway directions and may not be an efficient uniform wide-angle light source.

As such, what is desired is a LED light bulb that can uniformly emit light in most directions from the LED chip.

SUMMARY

This invention discloses an optical device for a semiconductor based lamp, the optical device comprising a base for mounting a semiconductor based light-emitting device thereon, a transparent body encapsulating the semiconductor based light-emitting device, and a reflective surface covering a predetermined region on a top of the transparent body, the reflective surface having an opening exposing the transparent body, wherein light emitted from the semiconductor based light-emitting device transmits through the opening of the reflective surface, meanwhile the reflective surface redirects some of the emitted light to lateral downward and in between directions.

The construction and method of operation of the invention, however, together with additional objectives and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings accompanying and forming part of this specification are included to depict certain aspects of the invention. A clearer conception of the invention, and of the components and operation of systems provided with the invention, will become more readily apparent by referring to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings, wherein like reference numbers (if they occur in more than one view) designate the same elements. The invention may be better understood by reference to one or more of these drawings in combination with the description presented herein.

FIG. 1 is a cross-sectional view of an optical device 100 for a semiconductor based lamp according to an embodiment of the present invention.

FIG. 2 illustrates the working mechanism of the optical device shown in FIG. 1.

FIG. 3A illustrates light travel paths in the optical device 100 shown in FIG. 1.

FIG. 3B illustrates an addition to the optical device 100 shown in FIG. 1 and associated light travel paths therein.

FIGS. 4A and 4B illustrate some design variations from the optical device 100 shown in FIG. 1.

FIGS. 5A-5D illustrate simulation results of the LED lamps of the present invention.

DESCRIPTION

The present invention discloses an optical device for a semiconductor based lamp. The optical device spreads semiconductor based lamp's directional light to directions of a wide angle, so that the light emitting pattern of the semiconductor based lamp resembles that of a traditional incandescent light bump.

FIG. 1 is a cross-sectional view of an optical device 100 for a semiconductor based lamp according to an embodiment of the present invention. The optical device 100 comprises a semiconductor based light emitting device 110 mounted on a base 120. A common type of the semiconductor based light emitting device 110 is light-emitting diodes (LEDs). The light emitting device 110 can be formed by either one LED or an array of LEDs. The light emitting surface of the light emitting device 110 is encapsulated by a transparent body 130. A reflective surface 140 is then formed on the top of the transparent body 130. The reflective surface 140 may have a slanted region 142 at an outer ring of the reflective surface 140. Optimally the reflective surface 140 is part of the top surface of the transparent body 130 that mirror reflects light from the light-emitting device 110 to a wide angle with high light intensity. The reflective surface 140 can be formed by plating a metal layer or by adhering a thin layer of sheet metal on top of the transparent body 130.

Referring to FIG. 1 again, the reflective surface 140 has an opening 145 that exposes approximately center portion of the transparent body 130 and hence center area of the light emitting device 110. The opening 145 allows light from the light-emitting device 110 to shine directly out of the transparent body 130.

As shown in FIG. 1, a boundary 135 of transparent body 130 in the opening 145 area has a special concave contour, which is designed, together with the reflective surface 140, to reflect some of the light from the light-emitting device 110 to lateral directions due to an optical phenomenon called “total internal reflection”.

FIG. 2 illustrates the mechanism of the total internal reflection. When light crosses a boundary 202 between materials with different refractive indices (n1 and n2), the light beam 210 will be partially refracted 218 at the boundary surface 202, and partially reflected 215. However, if the angle of incidence θ2 is greater (i.e. the ray is closer to being parallel to the boundary) than a critical angle—the angle of incidence at which light is refracted such that it travels along the boundary—then the light 220 will stop crossing the boundary 202 altogether and instead be totally reflected back 225 internally, i.e. total internal reflection occurs. This can only occur where light travels from a medium with a higher (n1=higher refractive index) to one with a lower refractive index (n2=lower refractive index). For example, it will occur when passing from glass to air, but not when passing from air to glass. The material for making the transparent body 130 can be glass or transparent polymer, such as acrylics, polycarbonate, poly (vinyl chloride), polyethylene terephthalate (PET).

FIG. 3A illustrates light travel paths in the optical device 100 shown in FIG. 1. Referring to FIG. 3A, a light beam 310 emitted from the outer area of the light-emitting device 110 hits the boundary 135 with a small angle of incidence, some of the light 310 is refracted into a light beam 315. Such refractive light 315 is the light that is transmitted directly from the light-emitting device 110.

Referring to FIG. 3 again, another light beam 320 emitted from the center area of the light-emitting device 110 hits the boundary 135 with a large angle of incidence to incur total internal reflection. As a result, the light beam 320 bounces off the boundary 135 and then the reflective surface 140 and is transmitted out of the transparent body 130 in a lateral direction as a light beam 325. Apparently the contour design of the boundary 135 along with the size of the opening 145 determines the amount of the light transmitted directly to the upright direction—represented by the light beam 315, and the amount of the light transmitted to the lateral direction—represented by the light beam 325. In general, the size of the opening 145 is smaller than that of the light-emitting device 110.

FIG. 3B illustrates an addition to the optical device 100 shown in FIG. 1 and associated light travel paths therein. Referring to FIG. 3B, the light emitting device 100 is alleviated by a platform 360. The platform 360 has slanted, reflective side walls 365. A light beam 330 hitting the reflective surface 140 is reflected into a lateral lighting beam 335. Another light beam 350 hitting the slanted region 142 of the reflective surface 140 is reflected downward thereby and then reflected again by the reflective side wall 365 of the platform 360, and ends up with a lateral light beam 355 with less downward angle.

FIGS. 4A and 4B illustrate some design variations from the optical device 100 shown in FIG. 1. Referring to FIG. 4A, an optical device 400 has the same light emitting device 110 as the optical device 100 of FIG. 1. But a transparent body 430 that encapsulates the light emitting device 110 has a center are protruding from an opening of a reflective surface 440. A cross-section of the protruding center area presents two convex regions 432 bordered by boundaries 435 and 437. The boundary 435 faces away from the center, and is exemplarily designed to be straight. The boundary 437 faces toward the center, and is exemplarily designed to be curved. A light beam 460 is total-internal reflected by the curved boundary 437 into a light beam 465 out of the transparent body 430. Apparently, the curved boundary 437 functions the same as the concave boundary 135 as shown in FIG. 3A. A light beam 450 is refracted through the straight boundary 435 into a light beam 455. With both the boundaries 435 and 437 controllable, light emitting pattern of the optical device 400 can be more optimized.

Referring to FIG. 4B, the optical device 400 has a frosted semi-transparent cover 480 that encloses the entire optical device 400. The frosted semi-transparent cover 480 enhances the uniformity of the emitted light.

FIGS. 5A and 5B illustrate simulation result of the LED lamp based on FIG. 3B of the present invention. Referring to FIG. 5A, a circular polar plot 500 shows far-field distribution (light intensity distribution) 502 and 504 on circular angular scale 506, with off-axis angle, with zero denoting the on-axis direction, and 180 degree the opposite direction, totally backward. This is possible for those preferred embodiments having some sideways extension so that 180 degree is unimpeded by the source. Referring back to FIG. 3B, a diameter of the LED device 110 is 20 mm. A diameter of the transparent body 130 is 38 mm. A distance between a top of the transparent body 130 and the surface of the LED device 110 is 8 mm. The far-field distribution 502 shows that light intensity below the LED device 110 has fairly large intensity. The far-field distribution 504 shows that light is also emitted to above the LED device 110.

Referring to FIG. 5B, a far-field distribution 520 is obtained when a frosted cover similar to the frosted cover 480 shown in FIG. 4B is placed over the LED lamp of FIG. 3B. The far-field distribution 522 shows that the light emitting pattern is close to a circle which means that light is emitted from the LED lamp uniformly in all directions.

FIGS. 5C and 5D illustrate simulation results of the LED lamps based on FIGS. 4A and 4B of the present invention. Referring to FIG. 5C, circular polar plot 540 shows far-field distribution (light intensity distribution) 542 and 544 on circular angular scale 506, with off-axis angle, with zero denoting the on-axis direction, and 180 degree the opposite direction, totally backward. Referring to FIG. 4A, a diameter of the LED device 110 is 20 mm. A diameter of the transparent body 130 is 38 mm. A distance between a top of the transparent body 130 and the surface of the LED device 110 is 11.83 mm. The far-field distribution 542 shows that light intensity at about 135 and 225 degree angle above the LED device 110 is very high. The far-field distribution 544 shows that light is also emitted to above the LED device 110.

Referring to FIG. 5D, a far-field distribution 560 is obtained when the frosted cover 480 is placed over the LED lamp as shown in FIG. 4B. The far-field distribution 562 shows that the light emitting pattern is close to a circle which means that light is emitted from the LED lamp uniformly in all directions.

The above illustration provides many different embodiments or embodiments for implementing different features of the invention. Specific embodiments of components and processes are described to help clarify the invention. These are, of course, merely embodiments and are not intended to limit the invention from that described in the claims.

Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims. 

1. An optical device for a semiconductor based lamp, the optical device comprising: a base for mounting a semiconductor based light-emitting device thereon; a transparent body encapsulating the semiconductor based light-emitting device; and a reflective surface covering a predetermined region on a top of the transparent body, the reflective surface having an opening exposing the transparent body, wherein light emitted from the semiconductor based light-emitting device transmits through the opening of the reflective surface.
 2. The optical device of claim 1, wherein the semiconductor based light-emitting device comprises at least one light-emitting diode (LED).
 3. The optical device of claim 1, wherein the opening is located at approximately a center area of the transparent body.
 4. The optical device of claim 1, wherein the transparent body has one or more concave boundaries at the area exposed by the opening.
 5. The optical device of claim 1, wherein the transparent body has one or more convex boundaries at the area exposed by the opening.
 6. The optical device of claim 1, wherein the transparent body is secured to the base.
 7. The optical device of claim 1, wherein the transparent body is made of a material selected from the group consisted of glass and polymer.
 8. The optical device of claim 1, wherein the reflective surface further comprises a slanted region that redirects light emitted from the semiconductor based light-emitting device downward.
 9. The optical device of claim 1, wherein the reflective surface is formed by plating a reflective material on the surface of the transparent body.
 10. The optical device of claim 1 further comprising a frosted semi-transparent cover enclosing the base and the transparent body.
 11. An optical device for a semiconductor based lamp, the optical device comprising: a base for mounting one or more light-emitting diodes (LEDs) thereon; a transparent body encapsulating the LEDs; and a reflective surface covering a predetermined region on a top of the transparent body, the reflective surface having an opening exposing the transparent body, wherein light emitted from the LEDs transmits through the opening of the reflective surface.
 12. The optical device of claim 11, wherein the opening is located at approximately a center area of the transparent body.
 13. The optical device of claim 11, wherein the transparent body has one or more concave boundaries at the area exposed by the opening.
 14. The optical device of claim 11, wherein the transparent body has one or more convex boundaries at the area exposed by the opening.
 15. The optical device of claim 11, wherein the transparent body is secured to the base.
 16. The optical device of claim 11, wherein the transparent body is made of a material selected from the group consisting of glass and polymer.
 17. The optical device of claim 11, wherein the reflective surface further comprises a slanted region that redirects light emitted from the LEDs downward.
 18. The optical device of claim 11, wherein the reflective surface is formed by plating a reflective material on the surface of the transparent body.
 19. The optical device of claim 11 further comprising a frosted semi-transparent cover enclosing the base and the transparent body. 